In a conventional one-side opening type filing apparatus, generally, a finger hook is provided for an accompanying plate which is pivotally attached to the side plate of a base plate through a spring and the accompanying plate is opened against the spring by hooking the finger to the finger hook. As an improved filing apparatus of such a one-side opening type filing apparatus in which the opening/closing member can be opened from any one of the right and left directions and the sheets can be filed and removed, there is a both-side opening type filing apparatus disclosed in Japanese Utility Model Registration Application No. 62-123979 laid open on Aug. 6, 1987. The above filing apparatus of the both-side opening type comprises: an attaching member in which coupling axial pipes are respectively provided at front and back positions of right and left side edges of a rectangular base plate; a pair of right and left hollow opening/closing members in which filing rods having a spike shape and a tubular shape which can be pierced each other are respectively attached at the front and back positions of the inner surface and axial pipes which are respectively coupled with the above axial pipes are provided along the lower edges; and coupling means arranged in the opening/closing members, wherein the coupling means is constructed by operating plates which are slidable in the front and back directions, a spring for always elastically pressing the operating plates in either one of the front and back directions, a pair of front and back coupling rods which are retained to the operating plates, and a locking member to lock the operative state of the operating plates. With the above construction, in the inoperative state, the pair of front and back coupling rods are set into the coupling state in which they are projected from the axial pipes of the opening/closing members into the axial pipes of the attaching member by the pressing force of the spring. When either one of the right and left operating plates is pressed and slided by the finger against the spring in such a coupling state, the coupling rods of retained to such an operating plate are escaped from the axial pipes of the attaching member, thereby disconnecting the axial pipes. The operating state is locked by the locking member. The other opening/closing member rotates to the attaching member and the above disconnected opening/closing member is away from the attaching member, thereby enabling the filing operation of the sheets or the like to be performed. According to the both-side opening type filing apparatus with the conventional construction as mentioned above, the filing operation of the sheets or the like can be performed by releasing the coupling state of the opening/closing members from any one of the right and left directions and it is convenient to use. However, since the operating plates are provided on the opening/closing member side, when the operating plate is pressed by the finger against the spring in order to remove the opening/closing member from the attaching member, the finger pressing force acts in a direction such as to restrict the operation of the opening/closing member which intends to be away from the attaching member, so that there is an inconvenience such that the operating efficiency of the opening/closing member is lost. Further, the cover plate has a distinction regarding the top and bottom from a viewpoint of the display of an index and a title. In the case of releasing the coupling state of the opening/closing members, it is most preferable to execute such a releasing operation on this side of the user. However, in the case of the foregoing construction, since the operating direction to release the coupling state of the opening/closing members is constant, in the case of attaching the filing apparatus to the cover plate, it is necessary to make the top/bottom directions of the cover plate coincident with the operating direction of the filing apparatus. Thus, there is a drawback such that the operating efficiency when the filing apparatus is attached to the cover plate is lost.